A technology that could reduce heat deaths: Trees

The trees were supposed to stay. It didn’t matter that the owners of the squat building alongside were planning to redevelop the property. The four eastern red cedars stood on city land, where they had grown for the better part of a century. “There’s no way these trees are coming down,” Shane McQuillan, who manages the city’s trees, recalled thinking. “The default position for us is, you don’t take out big trees to put in small trees.”

Here’s why: At a time when climate change is making heat waves more frequent and more severe, trees are stationary superheroes. Research shows that heat already kills more people in the United States than hurricanes, tornadoes and other weather-events, perhaps contributing to 12,000 deaths per year. Extreme heat this week in the Pacific Northwest and Canada has killed hundreds.

Trees can lower air temperature in city neighbourhoods 10 lifesaving degrees, scientists have found. They also reduce electricity demand for air conditioning, not only sparing money and emissions, but helping avoid potentially catastrophic power failures during heat waves.

“Trees are, quite simply, the most effective strategy, technology, we have to guard against heat in cities,” said Brian

Stone Jr., a professor of environmental planning at the Georgia Institute of Technology. So, in Des Moines, McQuillan worked with the property owners and city planners to find a way to redevelop while keeping the trees.

But one day several months later, he got word that a crew was taking them down. McQuillan raced to the site, just a couple blocks from his office. One tree had already been cut to a stump, and another was almost down. McQuillan halted the work and fought to stay calm. At first he assumed someone had taken matters into their own hands. But after investigating, he came to believe it was simply a mistake; the property had been leased for a restaurant and the tenants seemed sincerely unaware of the agreement. “There’s a defeated feeling,” McQuillan said. They were two losses in an enormous struggle. Versions of this story are playing out in cities across the country, according to the US Forest Service. Despite long-standing and ongoing efforts across the country to plant trees, communities in the United States are not adding to their total number or maintaining it. Research shows that American cities and towns lose the canopy of 36 mn trees every year.

Considering the cast of characters in Des Moines, its urban forest should be thriving. The longtime mayor is an environmentalist. The director of public works hails trees as “the only infrastructure that add value over time.” A non-profit group plants and tends the next generation of trees while giving green jobs and training to local teenagers. In recent years, though, the larvae of an iridescent green beetle that arrived from across the ocean, the emerald ash borer, have claimed 6,000 of the city’s 8,000 public ash trees.

A storm last year took out about 500 more of all kinds. Another big factor is the everyday losses: The tree felled to repair a water line underneath. The homeowner who removed a tree to build an extension or get more sun on the lawn. Countless new developments where trees were in the way. These are often mature trees whose canopy will take decades to replace. “It’s a challenge to get trees to thrive in the city,” said Phillip Rodbell, who leads a Forest Service team studying the social, economic and ecological impact of urban trees. At the same time, American cities are facing a heat crisis: The largest are warming at twice the rate of the planet as a whole.